The present invention relates to straddle cranes for carrying heavy and awkwardly sized loads, and more particularly, to straddle cranes of the type including a vertical column member at each of four corners thereof, two side beam members connected between respective pairs of vertical column members and at least one header beam member, with wheel or caster assemblies supporting each of the vertical column members.
Because of the heavy loads and shocks which are applied to the structural members and joints in straddle cranes, it is necessary to design carefully the structures and joints of the crane to accommodate such loads and to prevent structural failure so that minimum structural deformation occurs in the straddle crane structure when loaded and operated. Preferred designs require careful consideration of the member cross-sectional configurations and the connection means used between the various members.
U.S. Pat. No. 3,251,433 to Hintze et al. discloses a straddle type vehicle having spaced side frames connected by U-shaped members, a structure which is representative of a number of prior straddle vehicle structures. As the demand for greater load carrying capacities has increased, the basic structures have been modified by the additional use of various types of cross-bracing structures to strengthen the vehicle. In the main, such structures have been satisfactory where the vehicle travels over relatively planar ground or on a fixed track. When, however, the vehicle is required to traverse uneven terrain, as in the field, additional structural attention must be paid to the stresses which occur as the vehicle "walks" over the irregular terrain.
U.S. Pat. Nos. 3,640,413 and 3,356,239 disclose the use of load supporting members for torsionally and rotationally supporting a load engaging and supporting structure. By way of example, such load supporting members have not, however, heretofore been utilized effectively to provide a solution to the aforementioned problem nor have such members been used to join at their opposed ends respective pairs of vertical columns on a straddle vehicle.
Thus, it has remained a problem in the art to provide a straddle vehicle which includes two pairs of load-bearing columns with steerable casters at the lower ends of each column with sufficient structural integrity to accommodate heavy loads over uneven terrain. Specifically, the side beam member must under static and irregular terrain travel conditions provide a sufficient torsional and bending resistance to support the downward and inward load applied to the vertical columns by the upper reeving to engage the load, as well as a power package for the vehicle and an operator's station. In addition, a header beam member must provide a sufficient buckling resistance while yet being sufficiently flexible to provide for movement of the vehicle over irregular terrain without producing unacceptable shear stresses in the member. Thus, a broad overall objective of this invention is to provide a straddle vehicle of the type described which possesses the aforementioned desirable characteristics.
It is also preferable that the operator station and controls in a straddle crane vehicle be designed to facilitate versatile use and control of the vehicle by a single manual operator. Often, the visual attention of the operator is fully occupied during maneuvers with the need to observe clearances to prevent collisions with obstacles close to the desired path of travel. Accordingly, the steering and driving controls provided to the operator must permit optimal vehicle control to be achieved while requiring minimum attention or inputs from the operator.
While the operator station and the power package for the vehicle may be suspended beneath the side in an integrated package, these items may also be separated. Thus the power package can be located above or below the side beams and the operator located on a suspended column which pivots to provide the operator full vision in the direction of travel. Alternatively, the operator may be located in a cab above the side to provide vision over large objects.
It is also preferable to provide straddle cranes of the type adaptable for two-wheel or four-wheel steering, with two-wheel or four-wheel driving, with one open end or both ends closed. The structure of the invention permits the design of an open-ended straddle vehicle which does not require a rotating joint on one side of the machine to provide for the flexibility required for uneven terrain. Moreover, the manufacturer and the user have the option of adding a second header member, preferably identical to the first, to close the open end for different straddle lifting operations.
Accordingly, it is an object of the invention to provide an improved straddle vehicle structure better adapted to accommodate heavy loads and forces experienced during maneuvering over uneven or irregular surfaces.
It is a further object of the invention to provide a basic straddle crane structure which is adaptable for use for two-wheel or four-wheel steering and two-wheel or four-wheel driving, and to have either one open end or both ends closed.
It is still a further object of the invention to provide improved means for attaching the header beam member to the vertical column members of a straddle crane to better accommodate the stresses and forces experienced by the straddle crane during maneuvers over uneven and irregular surfaces.
It is another object of this invention to provide, in combination with a straddle vehicle having two pairs of vertical load-bearing columns with a header beam member as described, hollow torsion members secured by gussets between respective pairs of columns to provide torsional and bending resistance to the vehicle during traverse of irregular terrain.
It is a still further object of the invention to provide for improved positioning of the operator station on a straddle crane to permit the operator to have better visibility during maneuvering of the vehicle.
These and other objects and advantages will become apparent from a review of the written description of the invention taken with the accompanying drawings.